The invention relates to a drive mechanism for a motor vehicle windshield wiper device comprising a rotating crank arranged to rotate at least one wiper shaft, which accommodates a wiper arm of a windshield wiper and which is fixedly connected to at least one rocker arm. The rocker arm is connected to the crank via a drive rod wherein obstruction means are provided to allow evading movement of the drive rod in such a way that the crank can fully rotate unimpeded when the wiper is obstructed.
German Offenlegungsschrift 2,820,104 discloses a drive mechanism of this general type. There a wiper shaft has a windshield wiper rotationally fixed thereto and is connected to a rocker arm, which in turn is connected with a crank drive via a drive rod. In order to avoid obstruction of the windshield wiper in cases in which a snow wedge builds up (for example, in the wiper pocket of the windshield wiper), means are provided which enable the drive rod to pivot about a joint which connects the rocker and the drive rod, as a result of which, full rotation of the crank is made possible. A crank is rotationally fixed to the drive shaft and to a pivoted lever. One end of the pivoted lever is restrained by the crank through a spring element and its other end is guided along a curved slot recess which is provided on the crank. The pivoted lever is connected to the drive rod of the windshield wiper device. In the event of obstruction, the evading movement of the drive rod is produced by a fulcrum pin at the crank being swung inwards into the curved recess slot. As a result of this, the crank radius is reduced.
Another known drive mechanism which is used in single-arm wiper units, has a drive lever which is rotationally fixed to a wiper shaft and on which fulcrums are provided for articulated levers which are connected in the form of a crosslink to a drive rod. The drive rod is coupled to a rotating crank. A space-saving type of construction is obtained by a crosslink drive of this kind.
The object of the instant invention is to design a drive mechanism for a windshield wiper device of the above-mentioned general type in such a way that lower loading of the drive rod and its joints is obtained, even if the windshield wiper is obstructed by a snow wedge building up in the wiper pocket. Also the invention provides for a uniform wiping zone in normal wiping operations, despite forces occurring at the windshield wiper.
In a drive mechanism of the above-mentioned general type, this object is achieved by having the drive rod firmly coupled to the crank and the obstruction permitting means is arranged on the wiper shaft. The obstruction permitting means is so arranged as to allow an evading movement of the drive rod such that the joint connecting the crank to the drive rod is fixed relative to the crank and is guided on a constant crank radius. The design according to the invention ensures that forces occurring at the windshield wiper do not cause any change in the crank radius of the drive rod. In this way, when high torques can occur (especially in the case of large windshield wipers) and a uniform wiping movement is obtained in normal wiping operation, as a result of which an improvement in the cleaning capacity is achieved. A further advantage of placing the obstruction means on the wiper shaft is that when the windshield wiper is obstructed by a snow wedge building up in the wiper pocket, there is lower loading of the drive rod and its joints (in particular the rocker/drive-rod joint). It is also advantageous that a particularly space-saving arrangement is obtained with the drive mechanism according to the invention.
It is advantageous if the obstruction device consists of a first component, which is rotatably fixed on the wiper shaft and is connected to the drive rod and to a strap. A second component is rotatably fixed on the wiper shaft and has a slotted guide member for guiding the strap. By such an arrangement the obstruction compensation means consist essentially of four components, which results in a particularly simple construction. The strap is guided at its free end on the slotted guide which is provided on a second component rotationally fixed to the wiper shaft. The slotted guide is here designed such that in the event of obstruction by a snow wedge building up in the wiper pocket, the first component rotates relative to the second component. As a result, the drive rod is permitted to perform an evading movement and the crank is permitted to fully rotate.
A further development provides for a guide means which engages into a slotted guide to be provided on the strap. The guide means can be a roller.
In a further design, provision is made for a spring element which is restrained by the second component and which is coupled to the strap.
Provision can be made for the slotted guide to be provided with a catch recess in which the guide means can be detachably arrested. In the wiping position of the windshield wiper, in which the guide means of the strap engages into the catch recess, a particularly good connection of the first and second components relative to one another is thus obtained. In the event of obstruction, the guide means can come out of the catch recess and slide into another area of the slotted guide. This enables the first component to rotate relative to the second component.
The invention has the advantageous construction that allows for a two-arm wiper unit. Here the obstruction compensation device is arranged on a first wiper shaft with a second component and a rocker arm arranged on a second wiper shaft and the compensation device is connected to the second component via a connecting rod.
The slotted guide has a catch recess and a first guideway which makes possible an evading movement of the first component in a pivoting direction of the obstruction means for single wiper arms. The slotted guide has a catch recess, arranged centrally and with two guideways which make possible an evading movement of the first component into two pivoting directions to accommodate two wiper arms.
Another advantageous embodiment of the invention has two drive levers which are rotationally mounted on the wiper shaft to act as rocker arms. Each lever is connected to an articulated lever which in turn are connected in the form of a crosslink to the drive rod. The drive levers are restrained one against the other and have a recess into which a driving dog engages. The driving dog is connected to the wiper shaft such that the two drive levers are restrained with determinable play on the driving dog so that when movement of the windshield wiper is obstructed, an evading movement of the drive rod is made possible. It is desirable if the two drive levers are of the same type of design. The driving dog is arranged on a drive bushing which is rotatably fixed to the wiper shaft. The two drive levers are rotatably mounted on the drive bushing and are restrained at their recesses by the driving dog of the drive bushing.
In this latter embodiment, the two drive levers, rotationally connected on the wiper shaft, act as a rocker arm to which at least one articulated lever is coupled. The articulated levers are connected in the form of a crosslink to the drive rod. The drive levers are restrained against one another and each have one recess into which a driving dog, connected to the wiper shaft, engages. Here the two drive levers are restrained with determinable play on the driving dog such that, if the movement of the windshield wiper is obstructed, an evading movement of the drive rod is made possible. The articulated levers are arranged in the form of a crosslink to produce the pivoting movement in a pivoting direction of the windshield wiper. The recesses on the drive levers are dimensioned in such a way that full rotation of the crank in the event of obstruction is made possible. In this case, the position of the drive levers relative to one another is changed via one of the articulated levers. The size of the angle of rotation can be determined by the size of the recesses. The kinematics of the crosslink are designed such that the means respond only in the wiper pocket but not at the reduced wiping angle.
A further advantageous development of the invention provides for the two drive levers to be of the same type of design. The manufacturing costs of the novel drive mechanism are thereby reduced.
Another advantageous design provides for the driving dog to be arranged on a drive bush which is rotatably fixed to the wiper shaft.
It is also advantageous to have the driving dog and recesses hardened in their edge area.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.